Multilayer laminated circuit board

ABSTRACT

A multi-layer laminated circuit board  10 A of the present invention is formed by laminating together a multi-layer transformer  10 , a multi-layer part sheet  30  formed with a multi-layer part, and a wiring sheet  50  formed with a circuit pattern. The multi-layer transformer  10  is incorporated into the multi-layer laminated circuit board  10 A, and therefore a package for the multi-layer transformer  10  is omitted, and the wiring between the multi-layer transformer  10  and other components is reduced to a minimum.

TECHNICAL FIELD

The present invention relates to a multi-layer laminated circuit boardin the field of semiconductor technology, more specifically, relates tothat having an in-built multi-layer transformer in which a coil and coreare formed by stacking sheets having electromagnetic characteristics.

BACKGROUND ART

In recent years, multi-layer transformers have attracted attention thatare thin, small, and lightweight in accordance with rapid advances inthe miniaturization of electronic devices. FIG. 13 is a disassembledperspective view of a stacked body of a conventional multi-layertransformer. FIG. 14 is a vertical cross-sectional view along the lineXIV-XIV in FIG. 13 after stacking. The description below is based onFIGS. 13 and 14.

A conventional multi-layer transformer 80 comprises primary-windingmagnetic sheets 82 b and 82 d on which primary windings 81 a and 81 care formed, secondary-winding magnetic sheets 82 c and 82 e on whichsecondary windings 81 b and 81 d are formed, and magnetic sheets 82 aand 82 g that hold the magnetic sheets 82 b to 82 e from both sides.

Furthermore, a magnetic sheet 82 f for improving the magnetic saturationcharacteristic is inserted between the magnetic sheet 82 e and magneticsheet 82 g. The magnetic sheets 82 a to 82 e are provided withthrough-holes 90, 91, and 92 that connect the primary windings 81 a and81 c and through-holes 93, 94, and 95 that connect the secondarywindings 81 b and 81 d. The lower face of the magnetic sheet 82 a isprovided with primary-winding external electrodes 96 and 97 andsecondary-winding external electrodes 98 and 99. The through-holes 90 to96 are filled with a conductor. The magnetic sheets 82 a to 82 g are thecore of the multi-layer transformer 80.

Further, FIGS. 13 and 14 are schematic diagrams and, therefore, strictlyspeaking, the number of windings of the primary windings 81 a and 81 cand secondary windings 81 b and 81 d and the positions of thethrough-holes 90 to 96 do not correspond in FIGS. 13 and 14.

On the primary side of the multi-layer transformer 80, the current flowsin the order of the external electrode 96, through-hole 92, primarywinding 81 c, through-hole 91, primary winding 81 a, through-hole 90,and then the external electrode 97 or in the reverse order. On the otherhand, on the secondary side of the multi-layer transformer 80, thecurrent flows in the order of the external electrode 99, thethrough-hole 95, the secondary winding 81 d, the through-hole 94, thesecondary winding 81 b, the through-hole 93, and then the externalelectrode 98 or in the reverse order. The current flowing through theprimary windings 81 a and 81 c produces a magnetic flux 100 (FIG. 14) inthe magnetic sheets 82 a to 82 g. The magnetic flux 100 produces anelectromotive force corresponding with the winding ratio in thesecondary windings 81 b and 81 d. The multi-layer transformer 80operates thus.

Here, supposing that the self-inductance of the primary windings 81 aand 81 c is L1, the self-inductance of the secondary windings 81 b and81 d is L2, the mutual inductance of the primary windings 81 a and 81 cand the secondary windings 81 b and 81 d is M, and a magnetic couplingcoefficient k is defined by the following equation:k=|M|/√{square root over ( )}( L1·L2) (k≦1)

The magnetic coupling coefficient k is one of the indicators of thetransformer function and the larger the magnetic coupling coefficient k,the smaller the leakage magnetic flux (leakage inductance) becomes and,therefore, the power conversion efficiency is high.

Problem to Solved

The multi-layer transformer 80 is mounted on a printed wiring board asan individual component, for example. However, it is becoming more andmore difficult for such prior art to respond to demand for furtherreductions in the size of electronic equipment.

Further, in the multi-layer transformer 80, a magnetic layer (themagnetic sheets 82 c to 82 e) is formed between the primary windings 81a, 81 c and secondary windings 81 b, 81 d, causing magnetic flux leakage86 (FIG. 14), and hence it is not possible to obtain a sufficientelectromagnetic coupling coefficient k. To solve this problem, atechnique (referred to hereafter as a “conventional multi-layertransformer”) has been considered whereby a dielectric layer (not shown)is provided on the primary windings 81 a, 81 c and secondary windings 81b, 81 d by means of screen printing or paste coating such that themagnetic permeability of the magnetic layer is reduced by the substanceswhich diffuse from the dielectric layer.

However, in this conventional multi-layer transformer, conductivesubstances (Ag particles, for example) may diffuse from the primarywindings 81 a, 81 c and secondary windings 81 b, 81 d onto thedielectric paste coated on the primary windings 81 a, 81 c and secondarywindings 81 b, 81 d, leading to a decrease in the insulating propertybetween the primary windings 81 a, the primary windings 81 c, thesecondary windings 81 b, and the secondary windings 81 d. This isbecause the paste takes a liquid form due to an organic solvent or thelike, for example, and hence substances diffuse easily therefrom.

Moreover, when a dielectric layer is provided in order to reducemagnetic flux leakage, the gap between the primary windings 81 a, 81 cand secondary windings 81 b, 81 d corresponds to “the magnetic layer+thedielectric layer”, and therefore widens. As a result, magnetic fluxbecomes more likely to leak into the gap, causing the electromagneticcoupling coefficient k to decrease. Therefore, with this conventionalmulti-layer transformer, it is extremely difficult to increase theelectromagnetic coupling coefficient k.

OBJECT OF THE INVENTION

It is therefore a principal object of the present invention to provide atechnique for realizing a further decrease in the size of electronicequipment by maximizing the advantages of a small, light, thinmulti-layer transformer. A further object of the present invention is toprovide a multi-layer transformer in which an electromagnetic couplingcoefficient can be increased while maintaining an insulating propertybetween windings.

DISCLOSURE OF THE INVENTION

A multi-layer laminated circuit board according to the present inventioncomprises: an in-built multi-layer transformer formed by laminating amagnetic sheet, a primary winding and a secondary winding, and adielectric sheet constituted by a non-magnetic body; and a wiring sheetformed with a circuit pattern. In a preferred embodiment, the wiringsheet may be laminated onto an upper surface or a lower surface of themulti-layer transformer, or the multi-layer transformer may be providedon apart of the wiring sheet. The multi-layer laminated circuit boardmay further comprise a multi-layer part sheet formed with a multi-layerpart, or a thick film, a passive chip element, and an active chipelement may be mounted on a top surface thereof. In this case, eitherthe thick film, or the passive chip element, or the active chip elementmay be mounted on the top surface. Note that here, the “non-magneticbody” is a substance having a smaller magnetic permeability than atleast the magnetic sheet. The “dielectric sheet” is a sheet having agreater resistivity than at least the magnetic sheet, and may bereferred to as either a dielectric sheet or an insulating sheet.

In the prior art, the multi-layer transformer is mounted on a printedwiring board as an individual component. However, limits have beenreached in reducing the size of the multi-layer transformer package andreducing the amount of wiring between the multi-layer transformer andother components. Hence, in the present invention the multi-layertransformer is incorporated into the multi-layer laminated circuitboard. As a result, the multi-layer laminated circuit board is packaged,and therefore the multi-layer transformer package is omitted. Moreover,wiring can be provided in the lamination direction, leading to areduction in the surface area occupied by the wiring, and therefore thewiring between the multi-layer transformer and other components can bereduced to a minimum.

The multi-layer transformer that is incorporated into the multi-layerlaminated circuit board in a preferred embodiment of the presentinvention is constituted by the following laminated body. This laminatedbody comprises: a first magnetic sheet; a first dielectric sheetlaminated onto the first magnetic sheet and constituted by anon-magnetic body having a through hole formed in the center thereof; afirst winding positioned around the through hole on the first dielectricsheet and constituted by one or both of a primary winding and asecondary winding; a second magnetic sheet laminated onto the firstwinding so as to contact the first magnetic sheet on a peripheral edgeof and through the through hole in the first dielectric sheet; a seconddielectric sheet laminated onto the second magnetic sheet andconstituted by a non-magnetic body having a through hole formed in thecenter thereof; a second winding positioned around the through hole onthe second dielectric sheet and constituted by the other of, or both of,the primary winding and the secondary winding; and a third magneticsheet laminated onto the second winding so as to contact the secondmagnetic sheet on a peripheral edge of and through the through hole inthe second dielectric sheet. Further, the multi-layer transformer ispreferably formed by laminating together a plurality of these laminatedbodies such that the third magnetic sheet, excluding the third magneticsheet on an upper end, doubles as the first magnetic sheet of thelaminated body thereabove, and through holes respectively connecting theplurality of primary windings to each other and the plurality ofsecondary windings to each other are preferably provided in the magneticsheets and dielectric sheets.

The dielectric sheet has the following advantages over a dielectriclayer which is formed by coating the winding with a dielectric paste.(1) The dielectric sheet takes a solid form rather than a paste form andtherefore has a uniform film thickness regardless of the presence orabsence of a winding. As a result, a sufficient film thickness can besecured even in the parts where a winding is present. (2) Since thedielectric sheet is not in paste form, very little matter diffuses fromthe windings. As a result, the insulating property between the primarywindings and between the secondary windings does not deteriorate.

Further, a through hole is preferably formed in the center of thedielectric sheet, and the dielectric sheet is preferably formed to besmaller than the magnetic sheets. Thus, when the dielectric sheet issandwiched between the pair of magnetic sheets, the magnetic sheetscontact each other in the center and on the peripheral edge of thedielectric sheet such that the magnetic sheets form a core. Since thedielectric sheet is interposed between the primary winding and secondarywinding, an excellent insulating property can be realized.

The multi-layer transformer incorporated into the multi-layer laminatedcircuit board in a preferred embodiment of the present inventioncomprises: a dielectric sheet constituted by a non-magnetic body havinga through hole formed in the center thereof; a first winding positionedon one surface of the dielectric sheet and around the through hole, andconstituted by one or both of a primary winding and a secondary winding;a second winding positioned on the other surface of the dielectric sheetand around the through hole, and constituted by the other of, or bothof, the primary winding and the secondary winding; and a pair ofmagnetic sheets sandwiching the dielectric sheet, the first winding, andthe second winding, and contacting each other on a peripheral edge ofand through the through hole in the dielectric sheet.

The dielectric sheet may be constituted by a single sheet or a pluralityof laminated sheets. By disposing the primary winding and secondarywinding so as to face each other on either side of the dielectric sheet,a primary winding and a secondary winding may be disposed alternately onone surface of the dielectric sheet, and a primary winding and asecondary winding may be disposed alternately on the other surface ofthe dielectric sheet. When a plurality of dielectric sheets areprovided, a plurality of primary windings and secondary windings may beprovided on opposite sides of the dielectric sheets. In this case,through holes connecting the primary windings to each other andconnecting the secondary windings to each other may be provided in thedielectric sheets.

In the conventional multi-layer transformer, a magnetic layer is formedbetween the primary winding and secondary winding, and as a result, theelectromagnetic coupling coefficient is reduced by magnetic flux leakageinto the magnetic layer. Hence, in the multi-layer transformer of thepresent invention, a non-magnetic layer (the dielectric sheet) is formedbetween the primary winding and secondary winding. However, a core isnot formed simply by forming a non-magnetic layer, and therefore athrough hole is provided in the center of the dielectric sheet, and thepair of magnetic sheets are caused to contact each other through thethrough hole and on the peripheral edge of the dielectric sheet, therebyforming a core. Thus, in the multi-layer transformer of the presentinvention, a non-magnetic layer (the dielectric sheet) is formed betweenthe primary winding and secondary winding, and as a result, magneticflux leakage can be suppressed. Moreover, in contrast to theconventional multi-layer transformer, there is no need to form adielectric layer by coating the primary winding and secondary windingwith a dielectric paste, and hence the insulating property between theprimary windings and between the secondary windings does not deteriorateand the gap between the primary winding and secondary winding does notwiden.

In a preferred embodiment, the multi-layer transformer may furthercomprise a magnetic frame aligned with the peripheral edge of thedielectric sheet and a magnetic core aligned with the through hole, andthe pair of magnetic sheets may sandwich the dielectric sheet andcontact each other via the magnetic frame and magnetic core. In thiscase also, the dielectric sheet may be constituted by a single sheet ora plurality of (laminated) sheets. When a plurality of dielectric sheetsare provided, a plurality of primary windings and secondary windings areprovided on either side of the dielectric sheets. In this case, throughholes connecting the primary windings to each other and connecting thesecondary windings to each other may be provided in the dielectricsheets.

The dielectric sheet is preferably sandwiched between the first magneticsheet and second magnetic sheet, and the primary winding and secondarywinding are preferably positioned respectively on either surface of thedielectric sheet. The magnetic frame is aligned with the peripheral edgeof the dielectric sheet, and the magnetic core is aligned with thethrough hole in the center of the dielectric sheet. Thus there is littlesagging in the pair of magnetic sheets on the peripheral edge and in thecenter of the dielectric sheet. As a result, the pair of magnetic sheetsdo not have to be bent to a great extent, and therefore manufacture iseasy. Moreover, a magnetic path having a sufficient sectional area canbe secured, leading to an improvement in the magnetic saturationcharacteristic. This action becomes more striking as the number oflaminated dielectric sheets increases.

In particular, by matching the thickness of the magnetic frame (the sumtotal thereof when a plurality of magnetic frames are provided), thethickness of the magnetic core (the sum total thereof when a pluralityof magnetic cores are provided), and the thickness of the dielectricsheet (the sum total thereof when a plurality of dielectric sheets areprovided), an extremely even multi-layer transformer is obtained. Thus,when a wiring sheet is laminated onto the multi-layer transformer,warping of the wiring sheet can be suppressed, leading to an improvementin the reliability of the wiring sheet.

In a preferred embodiment, the magnetic frame and magnetic core may beconnected to each other via a support portion to form a magnetic sheet.In this case, the magnetic frame and magnetic core can be formedsimultaneously, and positioning thereof during lamination can also beperformed simultaneously.

The multi-layer transformer incorporated into the multi-layer laminatedcircuit board in a preferred embodiment of the present inventioncomprises: a composite sheet having a magnetic pattern in the center andon the peripheral edge thereof, and a dielectric pattern constituted bya non-magnetic body in parts other than the center and the peripheraledge; a first winding positioned on one surface of the dielectricpattern and around the center, and constituted by one or both of aprimary winding and a secondary winding; a second winding positioned onthe other surface of the dielectric pattern and around the center, andconstituted by the other of, or both of, the primary winding and thesecondary winding; and a pair of magnetic sheets sandwiching thecomposite sheet, the first winding, and the second winding, andcontacting each other via the magnetic patterns.

The composite sheet may be constituted by a single sheet or a pluralityof laminated sheets. By disposing the primary winding and secondarywinding so as to face each other on either side of the dielectricpattern on the composite sheet, a primary winding and a secondarywinding may be disposed alternately on one surface of the compositesheet, and a primary winding and a secondary winding may be disposedalternately on the other surface of the composite sheet. When aplurality of composite sheets are provided, a plurality of primarywindings and secondary windings may be provided on opposite sides of thecomposite sheets. In this case, through holes connecting the primarywindings to each other and connecting the secondary windings to eachother may be provided in the composite sheets.

In the conventional multi-layer transformer, a magnetic layer is formedbetween the primary winding and secondary winding, and as a result, theelectromagnetic coupling coefficient is reduced by magnetic flux leakageinto the magnetic layer. Hence, in the multi-layer transformer of thepresent invention, a non-magnetic layer (the dielectric pattern) isformed between the primary winding and secondary winding. However, acore is not formed simply by forming a non-magnetic layer, and thereforemagnetic patterns are provided in the center and on the peripheral edgeof the composite sheet, and the pair of magnetic sheets are caused tocontact each other through the magnetic patterns, thereby forming acore. Thus, in the multi-layer transformer of the present invention, anon-magnetic layer (the dielectric pattern) is formed between theprimary winding and secondary winding, and as a result magnetic fluxleakage can be suppressed. Moreover, in contrast to the conventionalmulti-layer transformer, there is no need to form a dielectric layer bycoating the primary winding and secondary winding with a dielectricpaste, and hence the insulating property between the primary windingsand between the secondary windings does not deteriorate and the gapbetween the primary winding and secondary winding does not widen.

In a preferred embodiment, the aforementioned composite sheet may beinterposed between the primary winding or secondary winding and themagnetic sheet. This composite sheet acts to enhance the insulatingproperty of the primary winding or secondary winding.

In a preferred embodiment, the film thickness of the magnetic patternsmay be equal to the film thickness of the dielectric pattern on thecomposite sheet. In this case, the film thickness of the composite sheetis constant in all locations, and therefore the pair of magnetic sheetssandwiching the composite sheet are also even. Thus, when a wiring sheetis laminated onto the multi-layer transformer, warping of the wiringsheet can be suppressed, leading to an improvement in the reliability ofthe wiring sheet.

According to the multi-layer laminated circuit board of the presentinvention, the multi-layer transformer is in-built, and therefore amulti-layer transformer package can be omitted and the wiring betweenthe multi-layer transformer and other components can be reduced to aminimum. As a result, the advantages of a small, light, thin multi-layertransformer can be maximized, enabling a further decrease in the size ofelectronic equipment.

According to the multi-layer transformer in the multi-layer laminatedcircuit board in a preferred embodiment of the present invention, thewindings are disposed on the dielectric sheet, and hence the filmthickness of the dielectric layer can be secured sufficiently even inthe parts where the windings are present. Moreover, the dielectric sheettakes a solid form rather than a paste form, and hence very littlematter is diffused from the winding into the dielectric sheet. As aresult, the insulating property between the primary windings and betweenthe secondary windings does not deteriorate. Accordingly, a greatimprovement in the insulating property between the windings can beachieved. Furthermore, the dielectric sheet having a through hole formedin its center is sandwiched between the pair of magnetic sheets suchthat the magnetic sheets contact each other in the center and on theperipheral edge of the dielectric sheet, and therefore the coreconstituted by the magnetic sheets has a simple constitution and can beformed by means of a straight forward method.

According to the multi-layer transformer in the multi-layer laminatedcircuit board in a preferred embodiment of the present invention, thedielectric sheet is provided between the primary winding and secondarywinding and a through hole is provided in the center of the dielectricsheet such that the pair of magnetic sheets contact each other throughthe through hole and on the peripheral edge of the dielectric sheet,thereby forming a core. As a result, a multi-layer transformer having anon-magnetic layer between the primary winding and secondary winding canbe realized, and therefore magnetic flux leakage can be suppressed.Moreover, in contrast to the conventional multi-layer transformer, thereis no need to form a dielectric layer by coating the primary winding andsecondary winding with a dielectric paste, and hence the insulatingproperty between the primary windings and between the secondary windingsdoes not deteriorate and the gap between the primary winding andsecondary winding does not widen. As a result, the electromagneticcoupling coefficient can be increased while maintaining the insulatingproperty between the windings. In addition, the insulating propertybetween the primary winding and the secondary winding is enhanced by theinterposition of the dielectric sheet in place of the conventionalmagnetic sheet.

In addition, according to the multi-layer transformer in the multi-layerlaminated circuit board in a preferred embodiment of the presentinvention, by having the pair of magnetic sheets which sandwich thedielectric sheet contact each other on the peripheral edge of andthrough the through hole in the dielectric sheet, the magnetic sheetsthemselves function as a magnetic core and a magnetic frame, andtherefore the number of components can be reduced.

According to the multi-layer transformer in the multi-layer laminatedcircuit board in a preferred embodiment of the present invention, themagnetic frame is aligned with the peripheral edge of the dielectricsheet, the magnetic core is aligned with the through hole in the centerof the dielectric sheet, and the magnetic frame and magnetic core aresandwiched between the pair of magnetic sheets. As a result, bending ofthe magnetic sheets on the peripheral edge and in the center of thedielectric sheet can be reduced. Hence, there is little or no need tobend the magnetic sheets, and therefore manufacture can be made easier.Moreover, a magnetic path having a sufficient sectional area can besecured, enabling an improvement in the magnetic saturationcharacteristic.

According to the multi-layer transformer in the multi-layer laminatedcircuit board in a preferred embodiment of the present invention, themagnetic frame and magnetic core are connected via a support portion toform a magnetic sheet, and hence the magnetic frame and magnetic corecan be formed simultaneously, and positioning thereof during laminationcan also be performed simultaneously. Thus manufacture can be madeeasier.

According to the multi-layer transformer in the multi-layer laminatedcircuit board in a preferred embodiment of the present invention, thedielectric pattern of the composite sheet is formed between the primarywinding and secondary winding, the magnetic patterns are formed in thecenter and on the peripheral edge of the composite sheet, and the pairof magnetic sheets contact each other through the magnetic patterns toform a core. As a result, a multi-layer transformer having anon-magnetic layer between the primary winding and secondary winding canbe realized, and magnetic flux leakage can be suppressed. Moreover, incontrast to the conventional multi-layer transformer, there is no needto form a dielectric layer by coating the primary winding and secondarywinding with a dielectric paste, and hence the insulating propertybetween the primary windings and between the secondary windings does notdeteriorate and the gap between the primary winding and secondarywinding does not widen. As a result, the electromagnetic couplingcoefficient can be increased while maintaining the insulating propertybetween the windings. In addition, the insulating property between theprimary winding and the secondary winding is enhanced by theinterposition of the dielectric pattern in place of the conventionalmagnetic sheet.

Further, by forming the dielectric pattern and magnetic patterns on asingle composite sheet, the number of sheets can be reduced and thelamination method can be simplified in comparison with a case in which adielectric sheet constituted by a dielectric body alone and a magneticsheet constituted by a magnetic body alone are laminated to form anidentical structure.

In addition, according to the multi-layer transformer in the multi-layerlaminated circuit board in a preferred embodiment of the presentinvention, by interposing an identical sheet to the aforementionedcomposite sheet between the primary winding or secondary winding and themagnetic sheet, the primary winding or secondary winding can beelectrically protected, and hence the insulating property can beenhanced.

According to the multi-layer transformer in the multi-layer laminatedcircuit board in a preferred embodiment of the present invention, thefilm thickness of the magnetic patterns and the film thickness of thedielectric pattern are equal, and therefore the film thickness of thecomposite sheet is constant in all locations. As a result, the pair ofmagnetic sheets sandwiching the composite sheet can be made even, andhence a circuit pattern or the like can be formed on the magnetic sheetswith a high degree of precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a first embodiment of amulti-layer laminated circuit board according to the present invention,and FIG. 2 is a longitudinal sectional view taken along a line II-II inFIG. 1 following lamination;

FIG. 3 is a partial sectional view showing a second embodiment of themulti-layer laminated circuit board according to the present invention,and FIG. 4 is a process drawing illustrating a manufacturing method forthe multi-layer laminated circuit board of FIG. 1;

FIG. 5 is an exploded perspective view showing a third embodiment of themulti-layer laminated circuit board according to the present invention,and FIG. 6 is a longitudinal sectional view taken along a line VI-VI inFIG. 5 following lamination;

FIG. 7 is an exploded perspective view showing a fourth embodiment ofthe multi-layer laminated circuit board according to the presentinvention, and FIG. 8 is a longitudinal sectional view taken along aline VIII-VIII in FIG. 7 following lamination;

FIG. 9 is an exploded perspective view showing a fifth embodiment of themulti-layer laminated circuit board according to the present invention,and FIG. 10 is a longitudinal sectional view taken along a line X-X inFIG. 9 following lamination;

FIG. 11 is an exploded perspective view showing a sixth embodiment ofthe multi-layer laminated circuit board according to the presentinvention, and FIG. 12 is a longitudinal sectional view taken along aline XII-XII in FIG. 11 following lamination;

FIG. 13 is an exploded perspective view showing a conventionalmulti-layer transformer, and FIG. 14 is a longitudinal sectional viewtaken along a line XIV-XIV in FIG. 13 following lamination.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 is an exploded perspective view showing a first embodiment of amulti-layer laminated circuit board according to the present invention.FIG. 2 is a longitudinal sectional view taken along a line II-II in FIG.1 following lamination. The following description is based on thesedrawings.

A multi-layer laminated circuit board 10A according to this embodimentis formed by laminating in sequence a multi-layer transformer 10, amulti-layer part sheet 30 on which a multi-layer part is formed, and awiring sheet 50 on which a circuit pattern is formed. In the multi-layerlaminated circuit board 10A, the multi-layer transformer 10 is in-built,and therefore a package for the multi-layer transformer 10 is omittedand the wiring between the multi-layer transformer 10 and othercomponents is reduced to a minimum. The reason for this is that theentire multi-layer laminated circuit board 10A is packaged, andtherefore a package for the multi-layer transformer 10 is not required.Further, since wiring can be provided in the lamination direction, thesurface area occupied by the wiring is reduced, and hence the wiringbetween the multi-layer transformer 10 and other components is reducedto a minimum. Moreover, the multi-layer transformer 10 may be providedon a part of the wiring sheet, as in a third embodiment to be describedbelow.

The multi-layer transformer 10 comprises a laminated body 15 a. Thelaminated body 15 a is constituted by: a magnetic sheet 11 a; a primarywinding dielectric sheet 13 a laminated onto the magnetic sheet 11 a andconstituted by a non-magnetic body having a through hole 12 a formed inthe center; a primary winding 14 a positioned around the through hole 12a on the dielectric sheet 13 a; a magnetic sheet 11 b laminated onto theprimary winding 14 a so as to contact the magnetic sheet 11 a on theperipheral edge of the dielectric sheet 13 a and through the throughhole 12 a therein; a secondary winding-forming dielectric sheet 13 blaminated onto the magnetic sheet 11 b and constituted by a non-magneticbody having a through hole 12 b formed in the center; a secondarywinding 14 b positioned around the through hole 12 b on the dielectricsheet 13 b; and a magnetic sheet 11 c laminated onto the secondarywinding 14 b so as to contact the magnetic sheet 11 b on the peripheraledge of the dielectric sheet 13 b and through the through hole 12 btherein.

Further, the magnetic sheets 11 a, 11 b and dielectric sheets 13 a, 13 bare provided with through holes 15, 16 for connecting the primarywinding 14 a and through holes 17, 18 for connecting the secondarywinding 14 b. Primary winding external electrodes 19, 20 and secondarywinding external electrodes 21, 22 are provided on the upper surface ofthe wiring sheet 50. Conductive bodies are inserted into the throughholes 15 to 18. The magnetic sheets 11 a to 11 c form the core of themulti-layer transformer 10.

The multi-layer part sheet 30 shown in the drawing is a low-pass filterfor blocking high-frequency noise using the secondary winding 14 b. Morespecifically, the multi-layer part sheet 30 comprises a dielectric sheet13 c for enhancing electric and magnetic insulation with regard to themulti-layer transformer 10, a multi-layer inductor 32 constituted bymagnetic sheets 11 d, 11 e and a coil winding 31, and a multi-layercapacitor 34 constituted by a high-permittivity dielectric sheet 13 dand parallel plate electrodes 33 a, 33 b. A current flowing through thecoil winding 31 generates magnetic flux 35 (FIG. 2) on the magneticsheets 11 d, 11 e. A voltage applied between the parallel plateelectrodes 33 a, 33 b causes a charge to accumulate in the parallelplate electrodes 33 a, 33 b.

The wiring sheet 50 is constituted by a dielectric sheet 13 e serving asan insulating substrate, and the external electrodes 19 to 22 of themulti-layer transformer 10, a wiring line 51, a component land 52, alaminated resistor 53, and so on formed on the upper surface of thedielectric sheet 13 e. A chip component 54 (FIG. 2) and so on aremounted on the component land 52.

Note that FIGS. 1 and 2 are schematic diagrams, and therefore the numberof turns and positions of the primary winding 14 a, secondary winding 14b, and coil winding 31, as well as the positions of the wiring line 51,component land 52, laminated resistor 53, and so on, do not correspondexactly between FIGS. 1 and 2. Furthermore, in FIG. 2 the film thicknessdirection (up-down direction) is enlarged to a greater extent than thewidth direction (left-right direction).

On the primary side of the multi-layer transformer 10, current flows ina sequence of external electrode 19→through hole 15→primary winding 14a→through hole 16→external electrode 20, or in a reverse sequencethereto. Meanwhile, on the secondary side of the multi-layer transformer10, current flows in a sequence of external electrode 21→through hole17→secondary winding 14 b→through hole 18→coil winding 31→through hole23→external electrode 22, or in a reverse sequence thereto. The currentflowing through the primary winding 14 a generates magnetic flux 24(FIG. 2) in the magnetic sheets 11 a to 11 c. The magnetic flux 24generates an electromotive force corresponding to the turns ratio in thesecondary winding 14 b. Thus the multi-layer transformer 10 functions.Note that the magnetic flux 24 does not interfere with the magnetic flux35 due to the interposition of the dielectric sheet 13 c.

The dielectric sheets 13 a and 13 b enhance the insulating property ofthe primary winding 14 a and secondary winding 14 b. Principally, thedielectric sheet 13 a enhances the insulating property between theprimary winding 14 a and the outside, while the dielectric sheet 13 benhances the insulating property between the primary winding 14 a andsecondary winding 14 b.

In the multi-layer transformer 10, the primary winding 14 a is disposedon the dielectric sheet 13 a, while the secondary winding 14 b isdisposed on the dielectric sheet 13 b. The dielectric sheets 13 a, 13 bhave the following advantages over a dielectric layer which is formeddirectly on a winding by coating the winding with a dielectric paste.(1) The dielectric sheet takes a solid form rather than a paste form andtherefore has a uniform film thickness regardless of the presence orabsence of a winding. As a result, a sufficient film thickness can besecured even in the parts where a winding is present. For convenience,in FIG. 2 the dielectric sheets 13 a, 13 b are shown to be indentedbeneath the primary windings 14 a and secondary windings 14 b. Inactuality, however, the film thickness of the dielectric sheets 13 a, 13b is uniform regardless of the presence or absence of a winding, asshown in FIG. 3. (2) Since the dielectric sheet is not in paste form,very little matter diffuses from the primary winding 14 a and secondarywinding 14 b. As a result, the insulating property between the primarywindings 14 a and between the secondary windings 14 b does notdeteriorate.

Note that by forming both the primary winding 14 a and the secondarywinding 14 b on the dielectric sheet 13 a, the magnetic sheet 11 c anddielectric sheet 13 b can be omitted. Furthermore, a dielectric sheetmay be interposed between the dielectric sheet 13 b and the magneticsheet 11 c to enhance the insulating property between the secondarywinding 14 b and the outside.

FIG. 3 is a partial sectional view showing a second embodiment of themulti-layer laminated circuit board according to the present invention.The following description is based on this drawing. Note, however, thatidentical reference symbols have been allocated to parts that areidentical to those of FIGS. 1 and 2, and description thereof has beenomitted.

A multi-layer transformer 60 in the multi-layer laminated circuit boardof this embodiment is constituted by further laminating laminated bodies15 b, . . . onto the laminated body 15 a. The magnetic sheet 11 c isshared by both of the laminated bodies 15 a and 15 b. Similarly to thelaminated body 15 a, the laminated body 15 b comprises magnetic sheets11 c, 11 f, 11 g, dielectric sheets 13 f, 13 g, a primary winding 14 c,and a secondary winding 14 d. Further, although not shown in thedrawing, through holes connecting the primary windings 14 a, 14 c. . .to each other and through holes connecting the secondary windings 14 b,14 d, . . . to each other are provided in the magnetic sheets 11 a, . .. and dielectric sheets 13 a, . . . .

The dielectric sheets 13 a, . . . enhance the insulating property of theprimary windings 14 a, 14 c and secondary windings 14 b, 14 d.Principally, the dielectric sheet 13 a enhances the insulating propertybetween the primary winding 14 a and the outside, the dielectric sheet13 b enhances the insulating property between the primary winding 14 aand the secondary winding 14 b, the dielectric sheet 13 f enhances theinsulating property between the secondary winding 14 b and the primarywinding 14 c, and the dielectric sheet 13 g enhances the insulatingproperty between the primary winding 14 c and the secondary winding 14d. The multi-layer transformer 60 of this embodiment exhibits similaractions and effects to the multi-layer transformer 10 of the firstembodiment.

Examples of the actual dimensions of each constitutional element willnow be given. The magnetic sheets 11 a, . . . have a film thickness of80 μm, a width of 8 mm, and a depth of 6 mm. The dielectric sheets 13 a,. . . have a film thickness of 40 μm, a width of 7 mm, and a depth of 5mm. The primary windings 14 a, . . . and secondary windings 14 b, . . .have a film thickness of 12 μm, a line width of 200 μm, and a linespacing of 150 μm. A practical number of laminated sheets constitutingthe multi-layer transformer 10, 60 is approximately 10 to 50 sheets.

FIG. 4 is a process drawing illustrating a manufacturing method for themulti-layer laminated circuit board of FIG. 1. The following descriptionis based on FIGS. 1 and 4.

First, a magnetic slurry is created (step 61). The magnetic material isan Ni—Cu—Zn type, for example. Next, a magnetic sheet is molded bymounting the magnetic slurry on a PET (polyethylene terephthalate) filmusing a doctor blade method (step 62). Next, the magnetic sheet is cutto obtain the magnetic sheets 11 a to 11 e (step 63). Alow-permittivity, non-magnetic slurry and a high-permittivity,non-magnetic slurry are then created separately in a similar fashion(step 64). A non-magnetic sheet is molded by mounting the non-magneticslurries on a PET film using a doctor blade method (step 65). Next, thenon-magnetic sheet is cut to obtain the dielectric sheets 13 c to 13 e(step 66). The dielectric sheets 13 c, 13 e have a low permittivity,while the dielectric sheet 13 d has a high permittivity.

Separately, a low-permittivity, non-magnetic paste (glass paste) iscreated (step 67). Next, the dielectric sheets 13 a, 13 b are created bymounting the non-magnetic paste onto a PET film using a screen printingmethod (step 68). Next, the through holes 15, . . . are formed in thedielectric sheets 13 a to 13 e and magnetic sheets 11 a to lie bypressing or the like (step 69). Next, the laminated resistor 53 isformed by screen-printing a resistive paste onto the dielectric sheet 13e alone (step 70). Next, an Ag type conductive paste is screen-printedto form the primary winding 14 a and secondary winding 14 b, the coilwinding 31, the wiring line 51, the component land 52, and so on, andalso to fill the through holes 15, . . . with a conductive body (step71).

Next, the magnetic sheets 11 a to 11 e and dielectric sheets 13 a to 13e obtained in the step 71 are peeled away from the PET films andlaminated together, whereupon the sheets are adhered tightly usingisostatic pressing to form the multi-layer laminated circuit board 10A(step 72). The multi-layer laminated circuit board 10A is then cut intoa predetermined size (step 73). Finally, co-firing is performed atapproximately 900° C. (step 74).

Note that the manufacturing method for the multi-layer laminated circuitboard of this embodiment applies to each of the following embodiments.Hence, description of the manufacturing method has been omitted from thefollowing embodiments.

FIG. 5 is an exploded perspective view showing a third embodiment of themulti-layer laminated circuit board according to the present invention.FIG. 6 is a longitudinal sectional view taken along a line VI-VI in FIG.5 following lamination. The following description is based on thesedrawings.

A multi-layer laminated circuit board 100 according to this embodimentis constituted by laminating a multi-layer transformer 110 onto a wiringsheet 101 formed with a circuit pattern. In the multi-layer laminatedcircuit board 100, the multi-layer transformer 110 is in-built, andtherefore a package for the multi-layer transformer 110 is omitted andthe wiring between the multi-layer transformer 110 and other componentsis reduced to a minimum. Note that the wiring sheet 101 may be laminatedonto the multi-layer transformer 110 in a similar fashion to the firstembodiment described above.

The wiring sheet 101 is constituted by a large number of laminateddielectric sheets 102 a, 102 b, 102 c, . . . External electrodes 122 to125 of the multi-layer transformer 110, a wiring line 103, a componentland 104, a laminated resistor 105, and so on are formed on the uppersurface of the uppermost dielectric sheet 102 a. A chip component 106(FIG. 6) and so on are mounted on the component land 104. A wiring line107, a through hole 108, a laminated resistor 109, and so on are formedon the internal dielectric sheets 102 b, 102 c, . . . (FIG. 6). Althoughnot shown in the drawing, a multi-layer capacitor and a multi-layerinductor are also formed on the wiring sheet 101.

The multi-layer transformer 110 comprises: a primary winding dielectricsheet 113 constituted by a non-magnetic body having a through hole 111 aformed in the center and a primary winding 112 formed on the peripheryof the through hole 111 a; a secondary winding dielectric sheet 115laminated onto the dielectric sheet 113 and constituted by anon-magnetic body having a through hole 111 b formed in the center and asecondary winding 114 formed on the periphery of the through hole 111 b;and magnetic sheets 116, 117 sandwiching the dielectric sheets 113, 115and contacting each other at the peripheral edges of the dielectricsheets 113, 115 and through the through holes 111 a, 111 b therein.

Further, the dielectric sheets 113, 114 and the magnetic sheet 116 areprovided with through holes 118, 119 for connecting the primary winding112 and through holes 120, 121 for connecting the secondary winding 114.Primary winding external electrodes 122, 123 and secondary windingexternal electrodes 124, 125 are provided on the lower surface of themagnetic sheet 116. Conductive bodies are inserted into the throughholes 118 to 121. The magnetic sheets 116, 117 form the core of themulti-layer transformer 110.

Note that FIGS. 5 and 6 are schematic diagrams, and therefore the numberof turns and positions of the primary winding 112 and secondary winding114, as well as the positions of the through holes 118 to 121, wiringline 103, component land 104, laminated resistor 105, and so on, do notcorrespond exactly between FIGS. 5 and 6. Furthermore, in FIG. 6 thefilm thickness direction (up-down direction) is enlarged to a greaterextent than the width direction (left-right direction).

On the primary side of the multi-layer transformer 110, current flows ina sequence of external electrode 122→through hole 118→primary winding112→through hole 119→external electrode 123, or in a reverse sequencethereto. Meanwhile, on the secondary side of the multi-layer transformer110, current flows in a sequence of external electrode 124→through hole120→secondary winding 114→through hole 121→external electrode 125, or ina reverse sequence thereto. The current flowing through the primarywinding 112 generates magnetic flux 126 (FIG. 6) in the magnetic sheets116, 117. The magnetic flux 126 generates an electromotive forcecorresponding to the turns ratio in the secondary winding 114. Thus themulti-layer transformer 110 functions.

In the multi-layer transformer 110, a non-magnetic layer (the dielectricsheet 115) is formed between the primary winding 112 and secondarywinding 114, and therefore magnetic flux leakage can be suppressed.Moreover, in contrast to the conventional multi-layer transformer, thereis no need to form a dielectric layer by coating the primary winding 112and secondary winding 114 with a dielectric paste, and hence theinsulating property between the primary windings 112 and between thesecondary windings 114 does not deteriorate and the gap between theprimary winding 112 and secondary winding 114 does not widen. As aresult, the electromagnetic coupling coefficient k can be increasedwhile maintaining the insulating property between the windings. Inaddition, the insulating property between the primary winding 112 andthe secondary winding 114 is enhanced by the interposition of thedielectric sheet 115.

The multi-layer transformer 110 of this embodiment is suitable for acase in which there is a small number of laminated dielectric sheets113, 114. The reason for this is that when the number of laminateddielectric sheets 113, 114 is small, the curvature at the bendingportions of the magnetic sheets 116, 117 decreases, and thereforemanufacture is easy and the magnetic layer has a sufficient thickness atthe center and peripheral edges thereof.

Note that by forming the primary winding 112 and secondary winding 114on either side of the dielectric sheet 115, the dielectric sheet 113 maybe omitted. The secondary winding 114 may be formed on the magneticsheet 117 instead of the dielectric sheet 115. A dielectric sheet may beinterposed between the secondary winding 114 and the magnetic sheet 117for enhancing the insulating property of the secondary winding 112. Whena plurality of dielectric sheets are laminated, magnetic sheets may beinterposed in certain locations. The dimensions of each constitutionalelement correspond to those of a fourth embodiment to be describedbelow.

FIG. 7 is an exploded perspective view showing a fourth embodiment ofthe multi-layer laminated circuit board according to the presentinvention. FIG. 8 is a longitudinal sectional view taken along a lineVIII-VIII in FIG. 7 following lamination. The following description isbased on these drawings.

The multi-layer laminated circuit board of this embodiment is identicalto those of the first and third embodiments except for a multi-layertransformer 130. Hence, only the multi-layer transformer 130 will bedescribed.

The multi-layer transformer 130 comprises: a primary winding dielectricsheet 133 constituted by a non-magnetic body having a through hole 131 aformed in the center and a primary winding 132 a formed on the peripheryof the through hole 131 a; a primary winding dielectric sheet 134constituted by a non-magnetic body having a through hole 131 b formed inthe center and a primary winding 132 b formed on the periphery of thethrough hole 131 b; a secondary winding dielectric sheet 137 laminatedonto the dielectric sheet 133 and constituted by a non-magnetic bodyhaving a through hole 135 a formed in the center and a secondary winding136 a formed on the periphery of the through hole 135 a; a secondarywinding dielectric sheet 138 laminated onto the dielectric sheet 134 andconstituted by a non-magnetic body having a through hole 135 b formed inthe center and a secondary winding 136 b formed on the periphery of thethrough hole 135 b; magnetic frames 139 a, 139 b aligned with theperipheral edges of the dielectric sheets 133, 134, 137, 138; magneticcores 140 a, 140 b aligned with the through holes 131 a, 131 b, 135 a,135 b; and magnetic sheets 141, 142 sandwiching the dielectric sheets133, 134, 137, 138 and contacting each other via the magnetic frames 139a, 139 b and magnetic cores 140 a, 140 b.

Further, the magnetic frame 139 a and magnetic core 140 a are connectedby four support portions 143 a to form a magnetic sheet 144. Themagnetic frame 139 b and magnetic core 140 b are connected by foursupport portions 143 b to form a magnetic sheet 145. A secondarywinding-protecting dielectric sheet 147 having the same size as thedielectric sheet 137 and formed with a through hole 146 a in its centeris interposed between the dielectric sheet 137 and magnetic sheet 144. Asecondary winding-protecting dielectric sheet 148 having the same sizeas the dielectric sheet 138 and formed with a through hole 146 b in itscenter is interposed between the dielectric sheet 138 and magnetic sheet145. Here, the term “winding protecting” means enhancing the insulatingproperty of the winding.

The dielectric sheets 133, 134, 137, 147 and the magnetic sheet 141 areprovided with through holes 149, 150, 151 for connecting the primarywindings 132 a, 132 b. The dielectric sheets 133, 134, 137, 138, 147 andthe magnetic sheet 141 are provided with through holes 152, 153, 154 forconnecting the secondary windings 136 a, 136 b. Primary winding externalelectrodes 155, 156 and secondary winding external electrodes 157, 158are provided on the lower surface of the magnetic sheet 141. Conductivebodies are inserted into the through holes 149 to 154. The magneticsheets 141, 142, 144, 145 form the core of the multi-layer transformer130.

Note that FIGS. 7 and 8 are schematic diagrams, and therefore the numberof turns in the primary windings 132 a, 132 b and secondary windings 136a, 136 b and the positions of the through holes 149 to 154 do notcorrespond exactly between FIGS. 7 and 8. Furthermore, in FIG. 7 thefilm thickness direction (up-down direction) is enlarged to a greaterextent than the width direction (left-right direction).

Examples of the actual dimensions of each constitutional element willnow be given. The magnetic sheets 141, 142, 144, 145 have a filmthickness of 100 μm, a width of 8 mm, and a depth of 6 mm. Thedielectric sheets 133, 134, 137, 138, 147, 148 have a film thickness of33 μm, a width of 7 mm, and a depth of 5 mm. The primary windings 132 a,132 b and secondary windings 136 a, 136 b have a film thickness of 15 μmand a line width of 200 μm. A practical number of laminated sheetsconstituting the multi-layer transformer 110, 130 is approximately 10 to50 sheets.

On the primary side of the multi-layer transformer 130, current flows ina sequence of external electrode 15→through hole 151→primary winding 132a→through hole 150→primary winding 132 b→through hole 149→externalelectrode 155, or in a reverse sequence thereto. Meanwhile, on thesecondary side of the multi-layer transformer 130, current flows in asequence of external electrode 157→through hole 154→secondary winding136 a→through hole 153→secondary winding 136 b→through hole 152→externalelectrode 158, or in a reverse sequence thereto. The current flowingthrough the primary windings 132 a, 132 b generates magnetic flux 159(FIG. 8) in the magnetic sheets 141, 142, 144, 145. The magnetic flux159 generates an electromotive force corresponding to the turns ratio inthe secondary windings 136 a, 136 b. Thus the multi-layer transformer130 functions.

In the multi-layer transformer 130, a non-magnetic layer (the dielectricsheets 134, 137, 138, 147) is formed between the primary windings 132 a,132 b and secondary windings 136 a, 136 b, and therefore magnetic fluxleakage can be suppressed. Moreover, in contrast to the conventionalmulti-layer transformer, there is no need to form a dielectric layer bycoating the primary windings 132 a, 132 b and secondary windings 136 a,136 b with a dielectric paste, and hence the insulating property betweenthe primary windings 132 a, the primary windings 132 b, the secondarywindings 136 a, and the secondary windings 136 b does not deteriorate,and the gaps between the primary windings 132 a, 132 b and the secondarywindings 136 a, 136 b do not widen. As a result, the electromagneticcoupling coefficient k can be increased while maintaining the insulatingproperty between the windings. In addition, the insulating propertybetween the primary windings 132 a, 132 b and the secondary windings 136a, 136 b is enhanced by the interposition of the dielectric sheets 137,138.

The multi-layer transformer 130 of this embodiment is suitable for acase in which there is a large number of laminated dielectric sheets133, . . . . The reason for this is that even though the number oflaminated dielectric sheets 133, . . . is large, the magnetic frames 139a, 139 b are aligned with the peripheral edges of the dielectric sheets133, . . . and the magnetic cores 140 a, 140 b are aligned with thethrough holes 131 a, . . . , and therefore the magnetic sheets 141, 142exhibit almost no bending. As a result, manufacture is easy and themagnetic layer has a sufficient thickness at the center and peripheraledge thereof.

Note that the magnetic frame 139 a and magnetic core 140 a may beprovided separately rather than being joined by the support portions 143a. This applies similarly to the magnetic frame 139 b and magnetic core140 b. The dielectric sheets 147, 148 may be omitted. Only one of themagnetic sheets 144, 145 need be provided.

FIG. 9 is an exploded perspective view showing a fifth embodiment of themulti-layer laminated circuit board according to the present invention.FIG. 10 is a longitudinal sectional view taken along a line X-X in FIG.1 following lamination. The following description is based on thesedrawings.

The multi-layer laminated circuit board of this embodiment is identicalto those of the first and third embodiments except for a multi-layertransformer 210. Hence, only the multi-layer transformer 210 will bedescribed.

The multi-layer transformer 210 comprises: a composite sheet 214 aconstituted by a central magnetic pattern 211 a and a peripheral edgemagnetic pattern 212 a formed respectively in the center and on theperipheral edge thereof, and a non-magnetic dielectric pattern 213 aformed in the parts other than the center and peripheral edge; acomposite sheet 214 b constituted by a central magnetic pattern 211 band a peripheral edge magnetic pattern 212 b formed respectively in thecenter and on the peripheral edge thereof, and a non-magnetic dielectricpattern 213 b formed in the parts other than the center and peripheraledge; a primary winding 215 a positioned on one surface of thedielectric pattern 213 a around the center thereof; a secondary winding215 b positioned on one surface of the dielectric pattern 213 b aroundthe center thereof; and a pair of magnetic sheets 216 a, 216 bsandwiching the composite sheets 214 a, 214 b, the primary winding 215a, and the secondary winding 215 b and contacting each other via thecentral magnetic patterns 211 a, 211 b and peripheral edge magneticpatterns 212 a, 212 b. In other words, it can be said that the primarywinding 215 a is positioned on the other surface of the dielectricpattern 213 b and the secondary winding 215 b is positioned on the firstsurface of the dielectric pattern 213 b.

Further, the composite sheets 214 a, 214 b and magnetic sheet 216 a areprovided with through holes 218, 219 for connecting the primary winding215 a and through holes 220, 221 for connecting the secondary winding215 b. Primary winding external electrodes 222, 223 and secondarywinding external electrodes 224, 225 are provided on the lower surfaceof the magnetic sheet 216 a. Conductive bodies are inserted into thethrough holes 218 to 221. The central magnetic patterns 211 a, 211 b,peripheral edge magnetic patterns 212 a, 212 b, and magnetic sheets 216,217 form the core of the multi-layer transformer 210.

Note that FIGS. 9 and 10 are schematic diagrams, and therefore thenumber of turns in the primary winding 215 a and secondary winding 215b, as well as the positions of the through holes 218 to 221, do notcorrespond exactly between FIGS. 9 and 10. Furthermore, in FIG. 10 thefilm thickness direction (up-down direction) is enlarged to a greaterextent than the width direction (left-right direction).

On the primary side of the multi-layer transformer 210, current flows ina sequence of external electrode 222→through hole 218→primary winding215 a→through hole 219→external electrode 223, or in a reverse sequencethereto. Meanwhile, on the secondary side of the multi-layer transformer210, current flows in a sequence of external electrode 224→through hole220→secondary winding 215 b→through hole 221→external electrode 225, orin a reverse sequence thereto. The current flowing through the primarywinding 215 a generates magnetic flux 226 (FIG. 10) in the magneticsheets 216 a, 216 b. The magnetic flux 226 generates an electromotiveforce corresponding to the turns ratio in the secondary winding 215 b.Thus the multi-layer transformer 210 functions.

In the multi-layer transformer 210, a non-magnetic layer (the dielectricpattern 213 b) is formed between the primary winding 215 a and secondarywinding 215 b, and therefore magnetic flux leakage can be suppressed.Moreover, in contrast to the conventional multi-layer transformer, thereis no need to form a dielectric layer by coating the primary winding 215a and secondary winding 215 b with a dielectric paste, and hence theinsulating property between the primary windings 215 a and between thesecondary windings 215 b does not deteriorate and the gap between theprimary winding 215 a and secondary winding 215 b does not widen. As aresult, the electromagnetic coupling coefficient k can be increasedwhile maintaining the insulating property between the windings. Inaddition, the insulating property between the primary winding 215 a andthe secondary winding 215 b is enhanced by the interposition of thedielectric pattern 213 b.

Further, on the composite sheet 214 a, the film thickness of the centralmagnetic pattern 211 a and peripheral edge magnetic pattern 212 a isequal to the film thickness of the dielectric pattern 213 a. Thisapplies similarly to the composite sheet 214 b. Hence, the filmthickness of the composite sheets 214 a, 214 b is constant in alllocations, and therefore the pair of magnetic sheets 216 a, 216 bsandwiching the composite sheets 214 a, 214 b are also even. On thecomposite sheet 214 a, the central magnetic pattern 211 a and peripheraledge magnetic pattern 212 a are formed on a single PET film by screenprinting and then peeled away from the PET film.

Note that by forming the primary winding 215 a and secondary winding 215b on either side of the composite sheet 214 b, the composite sheet 214 amay be omitted. The secondary winding 215 b may be formed on themagnetic sheet 216 b instead of the composite sheet 214 b. A compositesheet may be interposed between the secondary winding 215 b and themagnetic sheet 216 b to enhance the insulating property of the secondarywinding 215 b. The dimensions of each constitutional element correspondto those of a sixth embodiment to be described below.

FIG. 11 is an exploded perspective view showing a sixth embodiment ofthe multi-layer laminated circuit board according to the presentinvention. FIG. 12 is a longitudinal sectional view taken along a lineXII-XII in FIG. 11 following lamination. The following description isbased on these drawings.

The multi-layer laminated circuit board of this embodiment is identicalto those of the first and third embodiments except for a multi-layertransformer 230. Hence, only the multi-layer transformer 230 will bedescribed.

The multi-layer transformer 230 comprises: a primary winding-formingcomposite sheet 234 a constituted by a central magnetic pattern 231 aand a peripheral edge magnetic pattern 232 a formed respectively in thecenter and on the peripheral edge thereof, and a non-magnetic dielectricpattern 233 a formed in the parts other than the center and peripheraledge; a secondary winding-forming composite sheet 234 b constituted by acentral magnetic pattern 231 b and a peripheral edge magnetic pattern232 b formed respectively in the center and on the peripheral edgethereof, and a non-magnetic dielectric pattern 233 b formed in the partsother than the center and peripheral edge; a primary winding-formingcomposite sheet 234 c constituted by a central magnetic pattern 231 cand a peripheral edge magnetic pattern 232 c formed respectively in thecenter and on the peripheral edge thereof, and a non-magnetic dielectricpattern 233 c formed in the parts other than the center and peripheraledge; a secondary winding-forming composite sheet 234 d constituted by acentral magnetic pattern 231 d and a peripheral edge magnetic pattern232 d formed respectively in the center and on the peripheral edgethereof, and a non-magnetic dielectric pattern 233 d formed in the partsother than the center and peripheral edge; a secondarywinding-protecting composite sheet 234 e constituted by a centralmagnetic pattern 231 e and a peripheral edge magnetic pattern 232 eformed respectively in the center and on the peripheral edge thereof,and a non-magnetic dielectric pattern 233 e formed in the parts otherthan the center and peripheral edge; a primary winding 235 a positionedon one surface of the dielectric pattern 233 a around the centerthereof; a secondary winding 235 b positioned on one surface of thedielectric pattern 233 b around the center thereof; a primary winding235 c positioned on one surface of the dielectric pattern 233 c aroundthe center thereof; a secondary winding 235 d positioned on one surfaceof the dielectric pattern 233 d around the center thereof; and a pair ofmagnetic sheets 236 a, 236 b sandwiching the composite sheets 234 a to234 e, the primary windings 235 a, 235 c, and the secondary windings 235b, 235 d and contacting each other via the central magnetic patterns 231a to 231 e and peripheral edge magnetic patterns 232 a to 232 e.

In other words, it can be said that the primary winding 235 a ispositioned on the other surface of the dielectric pattern 233 b, thesecondary winding 235 b is positioned on the first surface of thedielectric pattern 233 b, the secondary winding 235 b is positioned onthe other surface of the dielectric pattern 233 c, the primary winding235 c is positioned on the first surface of the dielectric pattern 233c, the primary winding 235 c is positioned on the other surface of thedielectric pattern 233 d, and the secondary winding 235 d is positionedon the first surface of the dielectric pattern 233 d.

The composite sheets 234 a to 234 c and the magnetic sheet 236 a areprovided with through holes 240, 241, 242 for connecting the primarywindings 235 a, 235 c. The composite sheets 234 a to 234 d and themagnetic sheet 236 a are provided with through holes 243, 244, 245 forconnecting the secondary windings 235 b, 235 d. Primary winding externalelectrodes 246, 247 and secondary winding external electrodes 248, 249are provided on the lower surface of the magnetic sheet 236 a.Conductive bodies are inserted into the through holes 240 to 245. Thecentral magnetic patterns 231 a to 231 e, peripheral edge magneticpatterns 232 a to 232 e, and magnetic sheets 236 a, 236 b form the coreof the multi-layer transformer 230.

Note that FIGS. 11 and 12 are schematic diagrams, and therefore thenumber of turns in the primary windings 235 a, 235 c and secondarywindings 235 b, 235 d, as well as the positions of the through holes 240to 245, do not correspond exactly between FIGS. 11 and 12. Furthermore,in FIG. 12 the film thickness direction (up-down direction) is enlargedto a greater extent than the width direction (left-right direction).

Examples of the actual dimensions of each constitutional element willnow be given. The magnetic sheets 236 a, 236 b have a film thickness of100 μm, a width of 8 mm, and a depth of 6 mm. The composite sheets 234 ato 234 e have a film thickness of 50 μm, a width of 8 mm, and a depth of6 mm. The primary windings 235 a, 235 c and secondary windings 235 b,235 d have a film thickness of 15 μm and a line width of 200 μm. Apractical number of laminated sheets constituting the multi-layertransformer 210, 230 is approximately 10 to 50 sheets.

On the primary side of the multi-layer transformer 230, current flows ina sequence of external electrode 246→through hole 242→primary winding235 c→through hole 241→primary winding 235 a→through hole 240→externalelectrode 247, or in a reverse sequence thereto. Meanwhile, on thesecondary side of the multi-layer transformer 230, current flows in asequence of external electrode 249→through hole 245→secondary winding235 d→through hole 244→secondary winding 235 b→through hole 243→externalelectrode 248, or in a reverse sequence thereto. The current flowingthrough the primary windings 235 a, 235 c generates magnetic flux 250(FIG. 12) in the central magnetic patterns 231 a to 231 e, theperipheral edge magnetic patterns 232 a to 232 e, and the magneticsheets 236 a, 236 b. The magnetic flux 250 generates an electromotiveforce corresponding to the turns ratio in the secondary windings 235 b,235 d. Thus the multi-layer transformer 230 functions.

In the multi-layer transformer 230, a non-magnetic layer (the dielectricpatterns 233 b to 233 d) is formed between the primary windings 235 a,235 c and secondary windings 235 b, 235 d, and therefore magnetic fluxleakage can be suppressed. Moreover, in contrast to the conventionalmulti-layer transformer, there is no need to form a dielectric layer bycoating the primary windings 235 a, 235 c and secondary windings 235 b,235 d with a dielectric paste, and hence the insulating property betweenthe primary windings 235 a, the primary windings 235 c, the secondarywindings 235 b, and the secondary windings 235 d does not deteriorate,and the gaps between the primary windings 235 a, 235 c and the secondarywindings 235 b, 235 d do not widen. As a result, the electromagneticcoupling coefficient k can be increased while maintaining the insulatingproperty between the windings. In addition, the insulating propertybetween the primary windings 235 a, 235 c and the secondary windings 235b, 235 d is enhanced by the interposition of the dielectric patterns 234b to 234 d.

Further, on the composite sheet 234 a, the film thickness of the centralmagnetic pattern 231 a and peripheral edge magnetic pattern 232 a isequal to the film thickness of the dielectric pattern 233 a. Thisapplies similarly to the composite sheets 234 b to 234 e. Hence, thefilm thickness of the composite sheets 234 a to 234 e is constant in alllocations, and therefore the pair of magnetic sheets 236 a, 236 bsandwiching the composite sheets 234 a to 234 e are also even.

Needless to say, the present invention is not limited to the firstthrough sixth embodiments described above. For example, the number ofeach sheet type and the number of primary windings and secondarywindings may be determined arbitrarily. The primary winding andsecondary winding are not limited to a spiral shape, and may be formedby overlapping a large number of L shapes.

INDUSTRIAL APPLICABILITY

According to the multi-layer laminated circuit board of the presentinvention, a further decrease in the size of electronic equipment can berealized by maximizing the advantages of a small, light, thinmulti-layer transformer.

1. A multi-layer laminated circuit board characterized in comprising: anin-built multi-layer transformer formed by laminating a primary windingand a secondary winding, a dielectric sheet constituted by anon-magnetic body, and magnetic sheets provided so as to sandwich saiddielectric sheet and forming a core via a central through hole formed insaid dielectric sheet and a peripheral edge of said dielectric sheet;and a wiring sheet formed with a circuit pattern.
 2. The multi-layerlaminated circuit board according to claim 1, wherein said wiring sheetis laminated onto an upper surface or a lower surface of saidmulti-layer transformer.
 3. The multi-layer laminated circuit boardaccording to claim 1 or claim 2, wherein said multi-layer transformer isprovided on a part of said wiring sheet.
 4. The multi-layer laminatedcircuit board according to any of claims 1 through 3, further comprisinga laminated component sheet formed with a laminated component.
 5. Themulti-layer laminated circuit board according to any of claims 1 through4, wherein a thick film, a passive chip element, and an active chipelement are mounted on a top surface thereof.
 6. The multi-layerlaminated circuit board according to any of claims 1 through 5, whereinsaid multi-layer transformer is constituted by a laminated bodycomprising: a first magnetic sheet; a first dielectric sheet laminatedonto said first magnetic sheet and constituted by a non-magnetic bodyhaving a through hole formed in a center thereof; a first windingpositioned around said through hole on said first dielectric sheet andconstituted by one or both of a primary winding and a secondary winding;a second magnetic sheet laminated onto said first winding so as tocontact said first magnetic sheet on a peripheral edge of and throughsaid through hole in said first dielectric sheet; a second dielectricsheet laminated onto said second magnetic sheet and constituted by anon-magnetic body having a through hole formed in a center thereof; asecond winding positioned around said through hole on said seconddielectric sheet and constituted by the other of, or both of, saidprimary winding and said secondary winding; and a third magnetic sheetlaminated onto said second winding so as to contact said second magneticsheet on a peripheral edge of and through said through hole in saidsecond dielectric sheet.
 7. The multi-layer laminated circuit boardaccording to claim 6, wherein said multi-layer transformer is formed bylaminating together a plurality of said laminated bodies such that saidthird magnetic sheet, excluding said third magnetic sheet on an upperend, doubles as said first magnetic sheet of a laminated bodythereabove.
 8. The multi-layer laminated circuit board according to anyof claims 1 through 5, wherein said multi-layer transformer comprises: adielectric sheet constituted by a non-magnetic body having a throughhole formed in a center thereof; a first winding positioned on onesurface of said dielectric sheet and around said through hole, andconstituted by one or both of a primary winding and a secondary winding;a second winding positioned on the other surface of said dielectricsheet and around said through hole, and constituted by the other of, orboth of, said primary winding and said secondary winding; and a pair ofmagnetic sheets sandwiching said dielectric sheet, said first winding,and said second winding, and contacting each other on a peripheral edgeof and through said through hole in said dielectric sheet.
 9. Themulti-layer laminated circuit board according to claim 8, wherein saidmulti-layer transformer further comprises a magnetic frame aligned withsaid peripheral edge of said dielectric sheet and a magnetic corealigned with said through hole, and said pair of magnetic sheetssandwich said dielectric sheet and contact each other via said magneticframe and said magnetic core.
 10. The multi-layer laminated circuitboard according to claim 9, wherein said magnetic frame and saidmagnetic core are connected to each other via a support portion to forma magnetic sheet.
 11. The multi-layer laminated circuit board accordingto any of claims 1 through 5, wherein said multi-layer transformercomprises: a composite sheet having a magnetic pattern in a center andon a peripheral edge thereof, and a dielectric pattern constituted by anon-magnetic body in parts other than said center and said peripheraledge; a first winding positioned on one surface of said dielectricpattern and around said center, and constituted by one or both of aprimary winding and a secondary winding; a second winding positioned onthe other surface of said dielectric pattern and around said center, andconstituted by the other of, or both of, said primary winding and saidsecondary winding; and a pair of magnetic sheets sandwiching saidcomposite sheet, said first winding, and said second winding, andcontacting each other via said magnetic patterns.
 12. The multi-layerlaminated circuit board according to claim 11, wherein, in saidmulti-layer transformer, a composite sheet having a magnetic pattern ina center and on a peripheral edge thereof, and a dielectric patternconstituted by a non-magnetic body in parts other than said center andsaid peripheral edge, is interposed between said first winding or saidsecond winding and said magnetic sheets.
 13. The multi-layer laminatedcircuit board according to claim 11 or claim 12, wherein, on saidcomposite sheet, a film thickness of said magnetic patterns is equal toa film thickness of said dielectric pattern.